1. Field of Invention
This invention pertains to applications for bladder securement mechanisms for a tire press utilizing a position sensor mechanism, and more specifically to a method of utilizing an adjustable height bladder securement mechanism to effect advantageous tire shaping during the curing process.
2. Description of the Related Art
Tire presses and methods for making tires are well known in the art. FIG. 2 shows a green tire 12 undergoing a curing process in a tire press 10. The green tire 12 is placed within a cavity defined by a lower mold 14 and an upper mold 16. The lower mold 14 is fixedly installed on a base frame 18. The upper mold 16 can be closed and opened in relation to the lower mold 14. In FIG. 2, the tire press 10 is shown in the closed position.
A bladder securement mechanism 40, some aspects of which are currently known in the art, is illustrated in FIG. 1. The bladder securement mechanism 40 is commonly referred to as a “center mechanism.” In the bladder securement mechanism 40, a center mechanism tube 42 is supported by a guide cylinder 44, which is fixed on the base frame 18. The upper end (or first end) 32 of a bladder 30 is held by an upper clamping mechanism 70, which is attached to the upper end 48 of a center mechanism rod 46. The center mechanism rod 46 is positioned on a piston 50 of the center mechanism tube 42. A lower clamping mechanism 80, which holds the lower end (or second end) 34 of the bladder 30, is attached to the upper end of the center mechanism tube 42 through a hub 51. A pressurized fluid is supplied by way of a first port 52 formed in the lower part of the center mechanism tube 42 to a portion below the piston 50. The pressurized fluid is also supplied from a second port 54 through a pipe 56 to a portion on the top of the piston 50. The pipe 56 passes through the piston 50 and is inserted into the center mechanism rod 46.
The piston 50 and the center mechanism rod 46 move upward together. When the bladder 30 is deformed around the lower clamping mechanism 80, a heated pressurized medium such as steam is supplied through a fluid supply tube 58 via a through hole on the hub side into the bladder 30. Then the bladder 30 comes tightly into contact with the inner side of the green tire 12.
A floating piston 60 is adapted to contact the hub 51 and is slidably attached to the center mechanism rod 46. A stacking spacer 62 is positioned above the floating piston 60, and a stretch height spacer 64 is positioned below the floating piston 60 but above the piston 50. The stacking spacer 62 and the stretch height spacer 64 are exchangeably attached to the outside of the center mechanism rod 46. The stacking spacer 62 sets the lower limit position of the upper clamping mechanism 70 so that the upper clamping mechanism 70 is set to a shaping height corresponding to the tire size. The stretch height spacer 64 limits the upper clamping mechanism's 70 upward movement.
While suited for their intended purpose, present center mechanism designs of the tire curing presses have several disadvantages, which will now be described. The art does not address the bladder compounds, their resiliency, their thickness, or other variations that happen as the bladders age due to usage. As such, over time, bladders cease to maintain their original shape and size.
Further, as different sized tires are cured, the top clamp ring of the upper clamping mechanism must be repositioned to accommodate each tire size. This requires spacers of different lengths to be changed on the center mechanism. These spacers are cumbersome to change as different sized tires are cured. In addition, valuable production time is wasted. Also, since the spacers are generally fabricated from standard pipe, their lengths are not as precise as desired. Further, the spacers are subject to wear and tear over time, which leads to further imprecision and, thereby, possible imprecision in the tire.
Another problem with traditional spacers is that adjustment of the top ring is extremely limited during the curing process because the top clamping ring cannot advance towards the bottom ring once it has contacted the spacer. Still yet, another disadvantage of utilizing spacers is that the tire press only has two positions: open and closed. There is no mechanism for fine precision to ensure the green tire will cure correctly without any flaws or inaccuracies.
Present center mechanisms are limited in performance due to the restrictive nature of the spacers. For example, bladders utilized during the curing process must be discarded once their structural integrity has been degraded and/or the bladder has stretched to such a length that they cannot be used. Currently, there is no precise method of determining when the bladder has reached the end of its life. There is an economic incentive to use bladders for their full life cycle, so that bladders are changed less often.
Once bladders have been utilized over a certain number of curing cycles, they have been permanently stretched beyond their original length. As such, when the bladder securement mechanism is lowered to position the bladder against the green tire, there is excess bladder to position. However, since there are no controls used on most bladder securement mechanism designs, the bladder cannot be precisely controlled during the shaping process.
Also, during the curing process, an operator is “blind” as to the position of the upper clamping mechanism during the curing process. There is now way for the operator to finely tune the position of the top clamp ring of the upper clamping mechanism to ensure the cured tire will be free of defects.
Therefore, a need exists in the art for a center mechanism that operates without a spacer and that overcomes the foregoing difficulties and others. The present invention is contemplated to overcome these disadvantages by utilizing a linear position sensor with the bladder securement mechanism, such that the upper clamping mechanism may be moved at any time during the loading and shaping process. Having the ability to move the upper clamping mechanism offers safety and bladder insertion advantages.